Abstract
Methods for determining in situ stresses are reviewed, and a new approach is proposed for a better prediction of the in situ stresses. For theoretically calculating horizontal stresses, horizontal strains are needed; however, these strains are very difficult to be obtained. Alternative methods are presented in this paper to allow an easier way for determining horizontal stresses. The uniaxial strain method is oversimplified for the minimum horizontal stress determination; however, it is the lower bound minimum horizontal stress. Based on this concept, a modified stress polygon method is proposed to obtain the minimum and maximum horizontal stresses. This new stress polygon is easier to implement and is more accurate to determine in situ stresses by narrowing the area of the conventional stress polygon when drilling-induced tensile fracture and wellbore breakout data are available. Using the generalized Hooke’s law and coupling pore pressure and in situ stresses, a new method for estimating the maximum horizontal stress is proposed. Combined it to the stress polygon method, a reliable in situ stress estimation can be obtained. The field measurement method, such as minifrac test, is also analyzed in different stress regimes to determine horizontal stress magnitudes and calibrate the proposed theoretical method. The proposed workflow combined theoretical methods to field measurements provides an integrated approach for horizontal stress estimation.
Highlights
In situ stresses are consisted of the vertical stress and the maximum and minimum horizontal stresses
In an on-azimuth well of the Marcellus shale gas play, the productivity increased 40-50% compared to a 45° off-azimuth well [2]
We introduce some commonly used approaches to estimate in situ stresses, primarily the maximum and minimum horizontal stresses, provide an integrated method to calculate the horizontal stresses
Summary
In situ stresses are consisted of the vertical stress and the maximum and minimum horizontal stresses. We demonstrate that hydraulic fracturing in stage 2 in a vertical well was performed at the interface of two formations with high and low minimum horizontal stresses, respectively. The minimum and maximum horizontal stresses in the oil and gas industry are commonly estimated from borehole injection tests These data are generally unavailable in a new project (e.g., [6, 7]). We introduce some commonly used approaches to estimate in situ stresses, primarily the maximum and minimum horizontal stresses, provide an integrated method to calculate the horizontal stresses
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